The present invention relates to a turret tool post for a machine tool and an apparatus for controlling indexing of the same. More particularly, the present invention pertains to a turret tool post designed to enable ultra-high speed indexing and an apparatus for controlling the indexing process conducted by the turret tool post.
In the case of using a plurality of tools on a machine tool, it is common practice to use a turret tool post for indexing various tools successively, thereby efficiently conducting various kinds of machining operation without the need to change tools for each particular machining operation. More specifically, machining operations, for examples, turning, face milling, drilling, boring and threading, are efficiently carried out by successively indexing the required tools. There are known a variety of turret tool posts which may be classified into the following types: square turrets, hexagon turrets, flat turrets and drum-shaped turrets. If the indexing speed of a turret tool post is slow, the actual cutting time is shortened, which results in lowering of the cutting efficiency.
On the other hand, curvic coupling mechanism and knock pin mechanism wherein positioning is effected by insertion of a knock pin are known as indexing and positioning mechanisms for use in turret tool posts. Japanese Utility Model Unexamined Publication (Kokai) No. 62-95804 (1987) discloses a turret tool post for use in a machine tool or the like as being an intermittent indexing apparatus, which has a globoidal cam and a plurality of cam followers which are radially mounted on the peripheral surface of a shaft in such a manner as to be in engagement with the globoidal cam so that the cam followers are intermittently rotated to index and set a desired tool at a desired position.
The above-described conventional indexing and positioning mechanisms for a turret tool post need two operations, that is, an indexing operation and a clamping operation. The clamping operation is conducted in such a manner that, after the turret tool post has been rotated so as to reach a desired position, it is fixed in this position by oil-hydraulic or other similar driving means. Thus, there has heretofore been restriction on achievement of a reduction in the time needed for the indexing of the turret tool post that involves the above-described two operations.
The turret tool post that is disclosed in Japanese Utility Model Unexamined Publication (Kokai) No. 62-95804 (1987) set forth above does not need the above-described two operations. However, this turret tool post cannot provide discrete angles with a high degree of accuracy in indexing process unless both the cam shaft and the cam follower shaft are precisely positioned relative to each other. It is necessary in order to precisely provide a desired angle in indexing process to employ an apparatus for controlling the indexing process. Such a control apparatus is complicated as well as expensive. In addition, since there has recently been a demand for a high degree of positioning accuracy, it has heretofore been impossible to increase the indexing speed unconditionally.
Meanwhile, the body of a machine tool such as a lathe is covered with a machine cover for the reasons of design, safety and prevention of splash of cutting oil. The operator opens a door attached to the machine cover to replace a workpiece with another or change tools on the turret tool post. Accordingly, if the indexing speed of the turret tool post is increased, the operator is in danger when conducting an operation with the door of the machine cover kept open for effecting a setup or the like.